Production of light-colored leather.



UNITED STATES PATENT omnon.

SIGMOND SAXE, or NEW YORK, 1v. Y.

PRODUCTION OF LIGHT-COLORED LEATHER.

No Drawing.

To all whom it may concern:

Be it known that I, SreMoND SAxn, a citizen of the United States, residing at New York, county of New York, and State of New York, have invented certain new and useful Improvements in the Production of Light-Colored Leather; and I do hereby declare the following to be a full, clear, and exact description of the invention, such as will enable others skilled in the art to which it appertains to make and use the same.

This invention relates to a combined process of tanning and bleaching or improving the color of hides or skins which have already undergone a preliminary tanning treatment; and it comprises drumming or filling such hides with vegetable tanning materials or extracts in the presence of aluminum sulfate in any convenient form, the aluminum sulfate being employed most desirably in proportions of from five to ten per cent. of the weight of the extract employed. The invention is more fully set forth in the following description and claims.

A principal object of my invention is to produce a light colored leather by a procedure which eliminates or renders unnecessary the separate bleaching treatment ordinarily following the drumming operation in tanning processes as commonly practised heretofore. My new process enables a material saving in time and also effects a substantial saving in tanning materials, while the resulting leather is well bleached and is superior to leather produced according to the known processes and bleached in a separate step.

In tanning hides, especially for sole leather, it is well known that after the hide is tanned or struck through in the ordinary method of tanning, it is advantageous to drum the hide or fill the same by treating in a revolving drum with vegetable tanning materials or extracts. The revolving of the drum, containing the hide and the extract, causes the temperature to rise to a certain extent, or the temperature may be raised artificially, and the vegetable tanning mate rials are mechanically forced into the leather, thus giving the desired weight and color. At the same time a certain amount of the tanning material combines chemically with the hide substance. After this treatment, in order to improve the color of the leather, it is removed from the drum and Specification of Letters Patent.

Patented July 31, 1917.

Application filed August 11, 1915. Serial No. 44,988.

bleached by dipping, first, in a solution of an alkali, usually sodium carbonate in water, and then in an acid, usually dilute sulfuric acid. Or the leather after drumming is bleached in a liquid containing oxalic acid in solution, sulfites, or other bleaching liquor.

There are several objections to this method of bleaching. When the soda-sulfuric-acid bleach is used a very appreciable amount of the extracts or tanning materials put into the leather is removed by the bleaching process with consequent loss of weight. This is due to the fact that the alkali of the bleach combines chemically with the tannin in the hide, forming soluble compounds which wash out of the surface of the leather. Moreover in the usual separate bleaching treatments, considerable time and labor are required and the leather is sometimes injured to no slight extent by the harsh action of the chemicals employed.

I have discovered that the above disadvantages can be obviated and a good bleaching efi ect can be obtained by adding a relatively small proportion of aluminum sul-,

fate to the vegetable tanning materials or extracts when treating the leather or partially tanned hide in the drum. The aluminum sulfate may be added in any suitable form. Thus I may employ anhydrous aluminum sulfate; or, more conveniently, I may use the crystallized salt concentrated alum), Al (SO .1SH O; or I may employ ordinary potash alum. I use the term aluminum sulfate broadly to include all such substances. It is essential for the best results that the aluminum sulfate or alum be as free from iron as possible in order to avoid darkening and discoloring the leather. The proportions in which the aluminum sulfate is added may be varied within reasonable limits, but I find it most desirable to use a quantity approximately equal to between five and ten per cent. of the weight of the liquor in the drum.

In practice the proper amount of ironfree sulfate of alumina, or the equivalent amount of alum, is weighed out and dissolved in a small quantity of water and this solution may either be added to vegetable tanning material and thoroughly mixed therewith before placing in the drum, or the solution may be added after the treatment of the hides in the drum with vegetable tanning material has proceeded for a suitable time. The hides to be drummed with this mixture have been previously tanned or struck through according to any well known or suitable tanning method. 1 find that the best effects are produced when the drumming is conducted at a temperature around 100 F to 120 F although the method is not to be understood as narrowly limited in this respect. The time of drumming is about the same as in the ordinary methods of tanning in which the drumming is followed by the usual soda-sulfuric-acid bleach. I find that by carrying out my new process as above described, any insoluble precipitate which tends to be formed by reaction between the aluminum sulfate and the vegetable tans is either formed in. the leather itself, or else, if externally formed, is forced into the leather mechanically in the drumming. In either case there is substantially no loss of tans by precipitation. At the same time a good bleaching effect is obtained, rendering subsequent bleachingtreatment unnecessary, and the general appearance and character of the leather are very much improved.

I am aware that alum and sulfate of alumina have been used heretofore in the mineral tanning or tawing of hides; and also that socalled combination tannages of alum and certain vegetable tanning material, such as gambier and the like, are well known. My process is entirely different from such prior practice in that the sulfate of alumina is employed in fresh admixture with the vegetable tanning materials in the drumming operation, usually in relatively small proportions. In my process, the aluminum sulfate is primarily a bleaching or color-improving agent, and any tawing action which it may have is purely incidental and subordinate to its color-improw ing function. As to why alum has this bleaching effect I am not able to state definitely but content myself ith noting the fact.

lVhile as stated, it is most desirable to use from five to ten per cent. aluminum sulfate in the drum, it is not absolutely essential that the proportions employed be rigidly limited to this range of proportions. The advantages of the invention may be realized in part at least with proportions of alumi num sulfate as high as 15 per cent, or as low as 3 per cent, although I find the range above stated most satisfactory for ordinary work. I believe it to be broadly new, however, to fill and bleach partially tanned hide or leather in the drum with vegetable tanning liquor to which has been added aluminum sulfate.

The above description of my process is to be understood as merely illustrative of the principles upon which it is based, and various modifications of the specified procedure within the expected skill of the practical tanner may be made without departing from the spirit of the invention.

hat I claim is:

1. The hereindescribed process of producing light colored leather which comprises treating partially tanned hides in the drum with vegetable tanning material with which has been freshly admixed approximately from 5 to 10 per cent. of iron-free aluminum sulfate on the weight of the vegetable tanning material employed.

The hereindescribed process of producing light colored leather which comprises treating partially tanned hides in the drum with vegetable tanning material and freshly admixed aluminum sulfate until the hide is suitably filled and a bleaching action effected.

3. The hereindescribed process of producing light colored leather which comprises treating partially tanned hides with vegetable tanning material and a relatively small proportion of freshly admixed aluminum sulfate until the hide is suitably filled and a bleaching action effected.

4. The hereindescribed process of producing light colored leather which comprises drumming partially tanned hides with a vegetable tanning extract and not more than about 15 per cent. (on the weight of tanning material) of freshly admixed alumi num sulfate until the hide is suitably filled and a bleaching action effected.

5. The hereindescribed process of producing light colored leather which comprises first tanning or striking'through the hide in the usual manner and then filling the product and improving its color by drumming it with vegetable tanning material with which has been freshly admixed a relatively small percentage of aluminum sulfate.

In testimony whereof I hereunto affix my signature in th presence of two witnesses.

SIGMOND SAXE.

lVitnesses G. A. RArALLo, H. H. HURT.

Copies of this patent may be obtained for five cents each, by addressing the Commissioner of Patents, Washington, D. 0. 

